U.S. patent number 5,790,073 [Application Number 08/627,218] was granted by the patent office on 1998-08-04 for radio telecommunication network with fraud-circumventing registration.
This patent grant is currently assigned to Motorola, Inc.. Invention is credited to Scott David Blanchard, Joseph Olk Lester, Daniel Richard Tayloe, Dean Paul Vanden Heuvel, Johanna Alexandra Wild.
United States Patent |
5,790,073 |
Tayloe , et al. |
August 4, 1998 |
Radio telecommunication network with fraud-circumventing
registration
Abstract
A system (28) provides communication services to mobile units
(24). Mobile units (24) perform a unit-based location process (46,
48) to determine their locations. The system (28) performs a
system-based location process (64, 66) to independently determine
mobile unit locations. The system-based process may determine
location less precisely than the unit-based process. A location
selection process (104) evaluates the unit-determined location in
view of a system-determined location error region to decide whether
the unit-determined location is reliable. If the unit-determined
location is reliable, it is used (120) to qualify communication
services to be provided to the mobile unit (24). If the
unit-determined location is unreliable, the system-based process is
repeated (116) to improve the system-determined location precision,
and the resulting system-determined location is used (118) to
qualify communication services to be provided to the mobile unit
(24).
Inventors: |
Tayloe; Daniel Richard
(Phoenix, AZ), Vanden Heuvel; Dean Paul (Chandler, AZ),
Lester; Joseph Olk (Mesa, AZ), Blanchard; Scott David
(Mesa, AZ), Wild; Johanna Alexandra (Scottsdale, AZ) |
Assignee: |
Motorola, Inc. (Schaumburg,
IL)
|
Family
ID: |
24513730 |
Appl.
No.: |
08/627,218 |
Filed: |
March 13, 1996 |
Current U.S.
Class: |
342/357.2 |
Current CPC
Class: |
G01S
1/026 (20130101); H04B 7/1855 (20130101); G01S
5/12 (20130101) |
Current International
Class: |
G01S
1/02 (20060101); G01S 1/00 (20060101); G01S
5/14 (20060101); G01S 005/02 () |
Field of
Search: |
;342/357,457,450
;455/13.2,12.1 ;701/213 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tarcza; Thomas H.
Assistant Examiner: Phan; Dao L.
Attorney, Agent or Firm: Gorrie; Gregory J.
Claims
What is claimed is:
1. In connection with a radio telecommunication system that has a
satellite node and which provides communication services to mobile
units, a method of qualifying a mobile unit to utilize said
communication services, said method comprising the steps of:
performing, by said mobile unit, a first location process to
determine a first location for said mobile unit;
said mobile unit communicating said first location to said
system;
said radio telecommunication system performing a second location
process in response to communications conducted between said mobile
unit and said satellite node, said second location process
determining a second location for said mobile unit, said second
location having a second location error region; and
said radio telecommunication system deciding whether said first
location is reliable in response to said second location error
region by determining whether said first location resides within
said second location error region, and
when the first location is not reliable, the method additionally
includes the steps of:
repeating the step of said system performing the second location
process until said second location is within a predetermined
geolocation tolerance for said second location; and
granting system access to said mobile unit based on said second
location, and when said first location is reliable, the method
additionally includes the step of granting system access to said
mobile unit based on said first location.
2. A method as claimed in claim 1 additionally comprising the step
of configuring said first and second location processes so that
said first location has a first location error region associated
therewith, and said first location error region is smaller than
said second location error region.
3. A method as claimed in claim 1 wherein:
prior to providing communication services to said mobile unit, said
system associates mobile unit geolocation information with user
identity information; and
said method additionally comprises the step of using said first
location for said mobile unit geolocation information when said
deciding step decides that said first location is reliable.
4. A method as claimed in claim 1 wherein:
prior to granting access to said mobile unit, said system
associates mobile unit geolocation information with user identity
information; and
said method additionally comprises the step of determining, when
said deciding step decides that said first location is unreliable,
whether said second location error region betters said
predetermined geolocation tolerance.
5. A method as claimed in claim 4 wherein:
said second location process additionally determines a second
location for said mobile unit; and
said method additionally comprises the step of using said second
location for said mobile unit geolocation information when said
determining step determines that said first location is unreliable
and that said second location error region betters said
predetermined geolocation tolerance.
6. A method as claimed in claim 4 additionally comprising the step
of conducting additional location-determination communications
between said satellite node and said mobile unit when said
determining step determines that said first location is unreliable
and that said second location error region does not better said
predetermined geolocation tolerance.
7. A method as claimed in claim 1 wherein:
said system projects a plurality of communication cells over
diverse predetermined areas of the earth and each communication
cell has a unique identity;
said mobile unit is located in one of said communication cells;
said second location process identifies a time of arrival curve in
response to signal propagation delay between said mobile unit and
said satellite node and identifies said one communication cell;
and
said second location process defines said second location error
region to reside along an area defined as the intersection between
said one communication cell and said time of arrival curve.
8. A method as claimed in claim 1 wherein said satellite node moves
in an orbit around the earth, and said second location process
comprises the steps of:
identifying a time of arrival curve relative to a position for said
satellite node in response to signal propagation delay between said
mobile unit and said satellite node;
identifying a frequency of arrival curve relative to said position
for said satellite node in response to Doppler between said mobile
unit and said satellite node; and
defining said second location error region to reside in an area
located at the intersection of said time of arrival and frequency
of arrival curves.
9. A method as claimed in claim 1 wherein:
said method additionally comprises the step of determining, outside
said system, speed data for said mobile unit;
said method additionally comprises the step of sending said speed
data to said system;
said satellite node moves in an orbit around the earth; and
said second location process determines said second location error
region in response to Doppler detected in said communications
conducted between said mobile unit and said satellite node and
adjusted in response to said speed data.
10. A method as claimed in claim 9 additionally comprising the step
of refraining from communicating said speed data to said system
unless said speed data indicates a speed greater than a
predetermined speed.
11. A method as claimed in claim 9 wherein:
said determining step additionally determines a heading for said
mobile unit;
said sending step additionally sends said heading to said system;
and
said second location process additionally adjusts said Doppler in
response to said heading.
12. A method as claimed in claim 11 wherein:
said determining step additionally determines an elevation angle
for said mobile unit;
said sending step additionally sends said elevation angle to said
system; and
said second location process additionally adjusts said Doppler in
response to said elevation angle.
13. A method as claimed in claim 1 wherein said first location
process comprises the step of monitoring signals broadcast from a
plurality of transmitters remotely located from said mobile
unit.
14. In connection with a radio telecommunication system that has a
satellite node and which provides communication services to mobile
units, a method of qualifying a mobile unit to utilize said
communication services, said method comprising the steps of:
performing a first location process to determine a first location
for said mobile unit;
communicating said first location to said system;
performing a second location process in response to communications
conducted between said mobile unit and said satellite node, said
second location process determining a second location error region
for said mobile unit;
deciding whether said first location is reliable in response to
said second location error region;
configuring said first and second location processes so that said
first location has a first location error region associated
therewith, and said first location error region is smaller than
said second location error region;
associating mobile unit geolocation information with user identity
information prior to providing communication services to said
mobile unit;
using said first location for said mobile unit geolocation
information when said deciding step decides that said first
location is reliable, said mobile unit geolocation information
being better than a predetermined geolocation tolerance; and
determining, when said deciding step decides that said first
location is unreliable, whether said second location error region
betters said predetermined geolocation tolerance.
15. A method as claimed in claim 14 wherein:
said second location process additionally determines a second
location for said mobile unit, and
said method additionally comprises the steps of:
using said second location for said mobile unit geolocation
information when said determining step determines that said first
location is unreliable and that said second location error region
betters said predetermined geolocation tolerance; and
conducting additional location-determination communications between
said satellite node and said mobile unit when said determining step
determines that said first location is unreliable and that said
second location error region does not better said predetermined
geolocation tolerance.
16. A method as claimed in claim 15 wherein:
said system projects a plurality of communication cells over
diverse predetermined areas of the earth and each communication
cell has a unique identity;
said mobile unit is located in one of said communication cells;
said second location process identifies a time of arrival curve in
response to signal propagation delay between said mobile unit and
said satellite node and identifies said one communication cell;
and
said second location process defines said second location error
region to reside along an area defined as the intersection between
said one communication cell and said time of arrival curve.
17. A telecommunication system which selectively provides
communication services to a mobile unit, said system
comprising:
a satellite node configured to engage in communications with said
mobile unit; and
a system processor in data communication with said satellite node,
said system processor being configured to obtain a first location
for said mobile unit, said first location being determined by a
first location process performed by said mobile unit, to perform a
second location process to determine a second location having a
second location error region, said second location process being
performed by said system processor in response to said
communications with said mobile unit, and to decide whether said
first location is reliable in response to said second location
error region, by determining whether said first location resides
within said second location error region, and when the first
location is not reliable, the system processor repeats the second
location process until said second location is within a
predetermined geolocation tolerance for said second location and
grants system access to said mobile unit based on said second
location, and when said first location is reliable, the system
processor grants system access to said mobile unit based on said
first location.
18. A system as claimed in claim 17 wherein said system processor
is configured to decide whether said first location is reliable by
determining whether said first location resides within said second
location error region.
19. A system as claimed in claim 18 wherein said system processor
is configured to perform said first and second location processes
so that said first location has a first location error region
associated therewith and said first location error region is
smaller than said second location error region.
20. A system as claimed in claim 19 wherein said system processor
is configured to:
associate said system associates mobile unit geolocation
information with user identity information prior to providing
communication services to said mobile unit;
use said first location for said mobile unit geolocation
information when said system processor decides that said first
location is reliable; and
determine whether said second location error region betters said
predetermined geolocation tolerance when said first location is
unreliable.
21. A system as claimed in claim 20 wherein said system processor
is configured to:
perform said second location process that additionally determines a
second location for said mobile unit; and
use said second location for said mobile unit geolocation
information when it determines that said first location is
unreliable and that said second location error region betters said
predetermined geolocation tolerance.
22. A system as claimed in claim 21 wherein said system projects a
plurality of communication cells over diverse predetermined areas
of the earth and each communication cell has a unique identity,
said mobile unit is located in one of said communication cells, and
wherein said system processor is configured, as part of said second
location process, to:
identify a time of arrival curve in response to signal propagation
delay between said mobile unit and said satellite node and identify
said one communication cell;
define said second location error region to reside along an area
defined as the intersection between said one communication cell and
said time of arrival curve;
identify a frequency of arrival curve relative to said position for
said satellite node in response to Doppler between said mobile unit
and said satellite node; and
define said second location error region to reside in an area
located at the intersection of said time of arrival and frequency
of arrival curves.
Description
FIELD OF THE INVENTION
The present invention relates to radio telecommunications networks
which selectively qualify mobile subscriber units to receive
communication services based, at least in part, upon mobile unit
location.
BACKGROUND OF THE INVENTION
A system portion of cellular or other radio telecommunication
networks often needs to know the locations of the mobile subscriber
units for which communication services are to be provided. For
example, a system activates a ringing signal to alert a mobile unit
to an incoming call. If the system knows the location of the mobile
unit, then system resources can be conserved by activating the
ringing signal in only the area where the mobile unit is located.
System resources are conserved by refraining from activating the
ringing signal in areas where the mobile unit is not located.
When the system uses satellite base stations placed in moving
orbits around the earth, the need to know mobile unit locations
becomes even greater. Satellites may have coverage areas that
include geopolitical jurisdictions in which licenses to use the
electromagnetic spectrum have not been obtained or are different
from licenses for other jurisdictions. Accordingly, to comply with
differing spectrum licensing requirements imposed by different
geopolitical entities, the system may need to provide communication
services on one side of a geopolitical border but not on the other
side. This capability requires knowledge of mobile unit locations.
In addition, power consumption is a critical concern for electrical
equipment placed in satellites. Mobile unit location information
allows a satellite to minimize the amount of power used to deliver
a ringing signal to a targeted mobile unit.
The prior art discusses two mutually exclusive alternate techniques
by which the system may learn of mobile unit locations. In one
technique, the mobile unit determines its own location and sends
the location information to the system during a registration
process. The mobile unit may rely upon an independent location
determination system, such as the Global Positioning System (GPS),
in determining its location. In the alternate technique, the system
determines the location of the mobile unit based upon
communications conducted with the mobile unit. Doppler and
propagation delay of communication signals are measured, and
location is calculated in response to these measurements and in
response to known satellite position data.
The system-determined location technique is desirable for security
reasons. Since the system-determined location technique does not
rely solely upon information provided by mobile units, the
technique is not significantly vulnerable to fraud. In other words,
mobile units cannot successfully provide fraudulent location
information to gain system access which would otherwise be denied.
Unfortunately, a satellite constellation's geometry which is
optimized to provide communication services may not be optimized
for making location calculations. Consequently, such location
calculations tend to be imprecise unless they are based upon
numerous time-consuming communication signal measurements. In
addition, errors accrue in such calculations when mobile units are
traveling at higher speeds, and acceptable location precision may
not be achievable regardless of the number of signal measurements
taken. Imprecise location information may force the system to
improperly deny access to communication services, and the use of
numerous signal measurements undesirably consumes system resources
while degrading customer service by forcing users to wait for
registration to take place.
The mobile unit-determined location technique is desirable because
it conserves system resources and permits faster system access.
Only one communication needs to take place between a mobile unit
and the system. During this communication, the mobile unit informs
the system of its location, and its location can often be
determined accurately through the use of external location
determination systems. System resources are conserved since only
one communication takes place, and registration can occur quickly.
Unfortunately, this technique leaves the system vulnerable to
fraud.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention may be
derived by referring to the detailed description and claims when
considered in connection with the figures, wherein like reference
numbers refer to similar items throughout the figures, and:
FIG. 1 shows a layout diagram of an environment within which a
radio telecommunication network may operate;
FIG. 2 shows a cellular pattern formed on the surface of the earth
by a satellite portion of the network;
FIG. 3 shows a flow chart of a process performed by a mobile unit
portion of the network;
FIG. 4 shows a flow chart of a location determination
communications process performed at a satellite node of the
network;
FIG. 5 shows a flow chart of a location calculator process
performed at a system processor portion of the network;
FIG. 6 graphically depicts constant Doppler and constant
propagation duration curves which illustrate system location
determination; and
FIG. 7 shows a flow chart of a location selection process performed
at the system processor portion of the network.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a layout diagram of a radio telecommunication network
10 configured in accordance with a preferred embodiment of the
present invention. A constellation 12 consisting of several
satellite nodes 14 is placed in a relatively low orbit around the
earth 16.
One or more switching offices (SOs) 18 reside on the surface of the
earth and are in data communication with nearby ones of satellite
nodes 14 through RF communication links 20. SOs 18 couple to public
switched telecommunication networks (PSTNS) 22, from which calls
directed toward subscribers may be received and to which calls
placed by subscribers may be sent.
Network 10 also includes any number, potentially in the millions,
of subscriber units, hereinafter referred to as mobile units 24.
Mobile units 24 may be configured as conventional mobile or
portable radio communication equipment, but mobile units 24 may
alternatively be configured as stationary equipment. Mobile units
24 are configured to receive communication from satellite nodes 14
and to perform other functions which are discussed below.
Mobile units 24 determine their own locations. In one embodiment of
the present invention, mobile units 24 use a satellite positioning
system 26, such as the Global Positioning System (GPS), in making
this determination. Satellite positioning system 26 includes a
constellation of transmitting satellites which orbit the earth and
which continuously broadcast signals that may be monitored to
determine the location of the monitoring point. However, the
present invention is not limited to cooperation with the GPS
system. In alternative embodiments, mobile units 24 may receive
location information from on-board aircraft or ship navigation
systems, from Loran-C, or from their own calculations based on
monitoring transmissions from constellation 12 of satellite nodes
14.
Network 10 includes a communication system 28 through which mobile
units 24 communicate. In other words, communication system 28
includes equipment provided by, maintained by, and under the
control of a communication service provider. Communication system
28 is formed, at least in part, from constellation 12 of satellite
nodes 14 and SOs 18. Satellite nodes 14 and SOs 18 are in data
communication with one another, and many functions, such as
location determination calculations, performed by communication
system 28 may be performed at any node of communication system 28.
Due to non-geostationary orbits, (e.g., low earth orbits),
satellite nodes 14 constantly move relative to the earth. This
movement is highly predictable. Thus, communication system 28 knows
the locations of all satellites at any given point in time.
FIG. 2 shows a cellular footprint pattern 30 formed on the surface
of the earth by a single satellite node 14. Each satellite node 14
includes an array 32 of directional antennas. Each array 32
projects numerous discrete antenna patterns on the earth's surface
at numerous diverse angles away from its satellite node 14. FIG. 2
shows a diagram of a resulting pattern of cells 34 that a satellite
node 14 forms on the surface of the earth. Desirably, other
satellite nodes 14 (not shown) form other footprints (not shown) so
that cells 34 substantially cover the entire surface of the
earth.
For convenience, FIG. 2 illustrates cells 34 and footprint pattern
30 as being discrete, generally hexagonal shapes without overlap or
gaps. However, those skilled in the art will understand that in
actual practice equal strength lines projected from the antennas of
satellite nodes 14 may actually have a shape far different than a
hexagonal shape, that antenna side lobes may distort the pattern,
that some cells 34 may cover larger areas than other cells 34, and
that some overlap between adjacent cells may be expected.
Each cell 34 within footprint pattern 30 occupies a unique position
within footprint pattern 30. These positions are distinguished from
one another through the use of a cell ID, listed as 1 through 48 in
FIG. 2. A degree of imprecise location information may be obtained
by identifying a cell 34 that covers a position of interest. Such
location information roughly defines a position relative to a
satellite node 14. Since satellite nodes 14 orbit the earth in
predictable orbits, a satellite's position at a particular point in
time may be determined by combining the point in time with well
known orbital geometry. By combining a cell's position within a
footprint pattern 30 with the satellite's position, an imprecisely
specified location on the earth may be obtained. However, a
location specified in this matter may be accurate only within
hundreds of kilometers. Accordingly, this location determination
technique is too imprecise for use by communication system 28.
Each satellite node 14 is associated with a nadir direction. The
nadir direction is defined by an imaginary line (not shown)
extending from the satellite node 14 toward the center of the
earth. For a given satellite node 14, a ground point resides where
the nadir direction intersects the surface of the earth. As the
satellite node 14 moves around the earth in its orbit, this ground
point forms a satellite ground track 36.
On the surface of the earth, a boundary 38 separates a first
jurisdiction 40 from a second jurisdiction 42. Any number of
boundaries 38 may divide the entire earth's surface into any number
of different jurisdictions. Boundaries 38 need not represent
physical phenomena of the earth. Rather, boundaries 38 represent
lines imposed over the geography of the earth to achieve some of
the goals of network 10 (FIG. 1). Nothing prevents the existence of
more than one set of boundaries corresponding to the same sections
of the earth. Boundaries 38 may divide the earth into geopolitical
jurisdictions, communication service rate jurisdictions, local area
codes, and the like. Communication system 28 qualifies
communication services provided to a mobile unit 24 in accordance
with the one or more jurisdictions within which the mobile unit 24
resides. Accordingly, communication system 28 needs to know mobile
unit locations with sufficient precision so that it will, to a
degree of probability, accurately qualify communication services
provided to mobile units 24.
FIG. 3 shows a flow chart of a process 44 performed by a mobile
unit 24. Any number of mobile units 24 may individually perform
process 44. In general, process 44 includes a location
determination process which is performed outside communication
system 28 (FIG. 1) along with tasks which cooperate with an
independent location determination process performed by
communication system 28.
In particular, process 44 includes a task 46 that obtains location
data from a GPS receiver or other suitable source. The location
described by these data is referred to herein as a unit-determined
location or more simply as a unit location because it is determined
at or near mobile unit 24. Other suitable sources may include
aircraft navigation equipment, Loran-C, or a process which monitors
signals broadcast by satellite nodes 14 to determine a location for
mobile unit 24. Generally, GPS receivers and other sources of
location data monitor signals broadcast from transmitters remotely
located from mobile unit 24.
In addition, task 46 desirably obtains a definition for an error
region to associate with the location data. The error region
represents an area surrounding the reported unit location within
which mobile unit 24 most probably resides. Different geometries of
remote transmitters, different sources of location data, and other
differences may lead to different error regions for different
situations. However, many sources of location data resolve
locations to relatively small error regions. For example, basic GPS
receivers routinely provide location accuracy to within 0.1
kilometer.
In one embodiment, after task 46, task 48 obtains speed, heading,
and elevation angle data for mobile unit 24. Speed, heading, and
elevation angle data may be obtained directly from another source,
such as a GPS receiver or aircraft navigation equipment, or may be
calculated by monitoring changes in the unit location over time. In
another embodiment of the present invention, task 48 is
optional.
Next, a query task 50 determines whether a system or network access
event has occurred. A system access event, for example, may cause
mobile unit 24 to register or re-register with communication system
28. Registration allows communication system 28 to track the
movement of mobile unit 24 so that ring signals which alert mobile
unit 24 to incoming calls may desirably be broadcast in only the
area where mobile unit 24 resides. In addition, registration allows
communication system 28 to evaluate whether the current location of
mobile unit 24 still entitles mobile unit 24 to receive
communication services through communication system 28 for outgoing
calls. Typical network and system access events include an attempt
to make an outgoing call from mobile unit 24, moving mobile unit 24
a predetermined minimum distance away from the location at which
mobile unit 24 last registered with communication system 28, the
passage of a predetermined period of time since a previous
registration, and the like.
If task 50 determines that no system access attempt or registration
event has occurred, program flow loops back to task 46 to repeat
the unit location determination process and track movement of
mobile unit 24. As indicated by blocks in FIG. 3, any number of
additional tasks may be included in the program flow loop that
includes tasks 46, 48, and 50. For example, additional tasks may
test for attempts to initiate incoming calls or outgoing calls.
If task 50 detects a system access attempt or registration event, a
task 52 establishes communications with an overhead satellite node
14 (FIG. 1 and FIG. 2). Communications are established by
exchanging RF signals between mobile unit 24 and node 14. After
task 52, a task 54 causes mobile unit 24 to participate with the
node 14 in measuring Doppler and signal propagation delay in these
RF signals. Task 54 causes mobile unit 24 to participate in a
system location determination process which is independent of the
unit location determination process described above in connection
with tasks 46 and 48. The system location determination process is
discussed in more detail below.
Next, a query task 56 determines whether the speed of mobile unit
24 is greater than a predetermined threshold speed. As discussed
below in more detail, the preferred system location process may be
based, at least in part, upon Doppler in the RF signals exchanged
between mobile unit 24 and node 14. Doppler is responsive to the
relative velocity between node 14 and mobile unit 24. Accordingly,
mobile unit speed causes a Doppler offset relative to the Doppler
which would otherwise occur when mobile unit 24 is stationary, and
this Doppler offset translates into location error. In a preferred
system location process, location errors begin to become
significant when mobile unit 24 travels at around 70 miles per
hour, and become more significant the faster mobile unit 24
travels. Task 56 monitors speed data obtained above in task 48 to
determine whether mobile unit 24 is moving faster than a
predetermined threshold speed which may lead to unacceptable
location determination error.
If task 56 determines that mobile unit 24 is moving below the
threshold speed, a task 58 sends the location data obtained above
in task 46 along with error region data to communication system 28.
Thus, task 58 causes mobile unit 24 to communicate the unit
location to communication system 28. In one embodiment of the
present invention, if task 56 determines that mobile unit 24 is
moving above the threshold speed, a task 60 sends the location data
obtained above in task 46 along with error region data and the
speed, heading, and elevation angle data obtained above in task 48
to node 14. After task 58 or 60, process 44 causes mobile unit 24
to follow system instructions, as indicated at a task 62. Such
instructions may inform mobile unit 24 that a system access attempt
has been accepted or denied, and mobile unit 24 will respond
accordingly. Alternatively, such instructions may inform mobile
unit 24 that additional location determination communications are
required, and mobile unit 24 will repeat tasks 52 and 54 as
needed.
In one alternative embodiment to the above-discussed version of
process 44, tasks 48, 56, and 60 may be omitted for certain mobile
units 24, particularly when such mobile units 24 are configured so
that they are unlikely to travel at speeds in excess of the
threshold speed discussed above in connection with task 56. In this
situation, system-determined locations will not often be prone to
significant errors due to mobile unit speed. In another alternative
embodiment, tasks 56 and 58 may be omitted for mobile units 24
which are configured so that they are likely to travel at speeds in
excess of the threshold speed. In this situation, system-determined
locations will often be prone to errors caused by Doppler
offsets.
FIG. 4 shows a flow chart of a location determination
communications process 64 independently performed at satellite
nodes 14. FIG. 5 shows a flow chart of a location calculator
process 66 independently performed at system processors. The system
processors may, for example, be located at SOs 18, but system
processors may alternatively be located at node 14 or at any other
node of communication system 28 which is in data communication with
node 14. Generally, processes 64 and 66 together form the
above-discussed system-determined location process which resolves
the location of mobile unit 24 independently from the data
collected in task 46 (FIG. 3).
Referring to FIG. 4, location determination communication process
64 may be performed whenever a mobile unit 24 initiates a
communication with node 14, as discussed above in connection with
tasks 50 and 52 (FIG. 3). Process 64 includes a task 68 which
establishes communications with a mobile unit 24 by exchanging RF
signals between node 14 and mobile unit 24. Next, a task 70 records
a time stamp along with the ID of the cell 34 (FIG. 2) within which
communication is taking place, and other identity information. The
time stamp defines the point in time at which the location
determination communications will occur. As discussed above, the
cell ID may give an imprecise indication of location relative to
node 14. Other information may include data which identify the
particular node 14 engaging in the location determination
communications.
After task 70, a task 72 measures the Doppler of the communication
signals. This measurement may, for example, be made by first
synchronizing a frequency base used in transmitting a signal from
one of node 14 and mobile unit 24 and receiving the signal at the
other of node 14 and mobile unit 24. The frequency of the received
signal can then be measured to determine the frequency offset from
a predetermined frequency. However, any alternate Doppler
measurement technique known to those skilled in the art may be used
as well.
Next, a task 74 measures propagation delay of the location
determination signals. This measurement may be made by first
synchronizing a time base used in mobile unit 24 to the time base
of node 14, then transmitting a signal from one of node 14 and
mobile unit 24 and receiving the signal at the other of node 14 and
mobile unit 24. The received signal may then be measured to
determine any temporal offset from a predetermined point in time.
However, any alternate propagation delay measurement technique
known to those skilled in the art may be used as well.
While node 14 performs tasks 70, 72, and 74, mobile unit 24
participates in the measurements as needed, as discussed above in
connection with task 54 (FIG. 3). After task 74, a task 76 receives
the unit-determined location data along with related data such as
error region definition, speed, heading, and elevation angle, which
were discussed above in connection with tasks 58 and 60 (FIG. 3).
After task 76, a task 78 sends all measurements and location data
collected during process 64 to the system processor which will
calculate a system-determined location for mobile unit 24 and
select an appropriate location to use as a basis for qualifying
communication services to be delivered to mobile unit 24 by
communication system 28.
Referring to FIG. 5, location calculator process 66, performed by
the system processor, receives the measurements and location data
at a task 80. In a task 82, process 66 gets satellite ephemeris
data for the satellite node 14 taking the location determination
measurements. Such data may be obtained by applying the time stamp
and system node ID recorded above in task 70 (FIG. 4) to
conventional orbital geometry to obtain coordinates for the
satellite node 14 taking the location determination measurements.
Such ephemeris calculations may be worked out prior to task 82 and
saved in a table or other memory structure, or may be computed as
needed.
After task 82, a task 84 adjusts the Doppler measurement taken
above in task 72 (FIG. 4) to compensate for mobile unit speed,
heading, and elevation angle. Of course, if speed, heading, and
elevation angle are not known, then task 84 may be omitted.
Likewise, Doppler adjustments may still be made if fewer than all
of these parameters are known. Generally speaking, the speed,
heading, and elevation angle parameters define a velocity vector
which may be added to a velocity vector obtained from the ephemeris
data obtained above in task 82 using vector addition.
After task 84, a task 86 identifies at least one frequency of
arrival curve which fits the adjusted Doppler data. A given Doppler
measurement can be reported from any point located on a curve
geographically centered generally about satellite ground track 36
(FIG. 2) and extending away from the satellite node 14.
FIG. 6 graphically depicts constant Doppler curves 88. As shown in
FIG. 6, a given Doppler component may be graphically plotted on the
surface of the earth as a parabola generally centered along ground
track 36. The given Doppler component extends away from a satellite
node 14. Higher Doppler rates result in thinner parabola-like
curves 88. At zero Doppler, which occurs when a satellite node 14
is directly overhead a mobile unit 24, the Doppler curve has an
infinite width and resembles a straight line perpendicular to
ground track 36. The frequency of arrival (FOA) parabola or curve
determined in task 86 (FIG. 5) represents the curve 88 that
describes the Doppler component indicated in the measurement
record.
Referring back to FIG. 5, after task 86 determines the frequency of
arrival curve on the surface of the earth, a task 90 determines a
time of arrival circle which fits the propagation duration data
measured above in task 74. Since electromagnetic signals propagate
through the atmosphere at a constant velocity of approximately the
speed of light, a given propagation duration dictates that the
source of a signal responsible for the propagation duration must
reside on the surface of a sphere having a radius approximately
equal to the propagation duration times the speed of light and
centered at the point where the signal is received. In the present
invention, the source of an electromagnetic signal may be a mobile
unit 24 residing on or near the surface of the earth and the signal
may be received at a satellite node 14 orbiting the earth. Thus, a
time of arrival circle represents the intersection of a sphere,
centered at satellite node 14 and having a radius equivalent to the
speed of light times the propagation duration, with the earth's
surface.
FIG. 6 graphically depicts constant time of arrival (TOA) circles
or curves 92. As shown in FIG. 6, a given propagation duration may
be graphically plotted on the surface of the earth as a circle
centered at the point on ground track 36 where the satellite's
nadir direction intersects the surface of the earth. Longer
propagation durations result in circles having larger radii. The
TOA curve determined in task 90 (FIG. 5) represents the circle TOA
curve 92 that describes the propagation duration indicated in the
measurement record.
The intersection of FOA curve 88 determined in task 86 with the TOA
curve 92 determined in task 90 provides a two-position solution to
the location determination problem, as graphically illustrated in
FIG. 6. One position from each two-position solution resides to the
right of satellite ground track 36 and the other resides to the
left of satellite ground track 36. Referring back to FIG. 5, after
tasks 86 and 90 have determined frequency and time of arrival
curves 88 and 92, a task 94 calculates a system-determined location
for mobile unit 24 using FOA curve 88 and TOA curve 92. This system
location is determined to be one of the two intersections of the
FOA curve 88 with the TOA curve 92. The appropriate one of the two
solutions may, for example, be determined by evaluating cell
ID.
Next, a task 96 estimates a system location error region to be
associated with the system location calculated above in task 94. As
illustrated in FIG. 6, the error region depends in part upon the
geometry of satellite node 14 and mobile unit 24 at the instant
measurements are being made. A relatively large system location
error region 98 results when mobile unit 24 resides near ground
track 36. At such locations, FOA curves 88 become more tangential
to TOA curves 92, and their intersection cannot be determined with
precision. On the other hand, a relatively smaller system error
region 100 results when mobile unit 24 resides farther away from
ground track 36. At these locations, FOA curvess 88 become more
perpendicular to TOA curves 92, and their intersection can be
determined more precisely. Moreover, the error is typically greater
in a direction perpendicular to ground track 36 than in a direction
parallel to ground track 36. Together, these factors suggest that
the system location probably does not describe the actual location
for mobile unit 24, but that the actual location resides somewhere
within system location error region 98 or 100.
Referring back to FIG. 5, program flow exits process 66 after task
96. A system location has been calculated independently of location
data provided by mobile unit 24, and a system location error region
has been calculated to go along with the system location.
FIG. 2 graphically illustrates an alternate embodiment to the
version of location calculator process 66 specifically illustrated
in FIG. 5. In this alternate embodiment, Doppler-related tasks,
such as task 84 and 86 may be omitted while retaining propagation
delay-related tasks, such as task 90. Tasks 94 and 96 calculate an
intersection between the TOA curve 92 and a cell area corresponding
to the cell ID. FIG. 2 graphically illustrates a system location
error region 102 which represents a stripe through the cell, which
is cell ID 17 in this example, where location determination
communications with mobile unit 24 took place. The system location
may be estimated to be midway between cell boundaries within region
102. While this alternative embodiment may not yield system
location error regions as small as are obtained using Doppler
calculations, it is not sensitive to Doppler offset errors caused
by mobile unit speed. Accordingly, there is improved fraud
detection performance when compared to the use of the beam
footprint.
FIG. 7 shows a flow chart of a location selection process 104
desirably performed at the same system processor which performs
location calculator process 66 (FIG. 5). Generally, process 104
determines whether the unit location is reliable and provides an
appropriate geolocation parameter upon which communication system
28 may base communication service qualifications whether or not the
unit location is reliable.
Process 104 includes a task 106 which gets the unit-determined
location data discussed above in connection with FIG. 3. Next, a
task 108 gets the system location error region 98, 100, or 102
determined above in connection with task 96 (FIGS. 2, 5, and 6).
After task 108, a query task 110 determines whether the unit
location is reliable in view of the system location error region.
In particular, task 110 may decide whether the unit-determined
location resides within the system-determined location error
region. If the unit location resides within the system location
error region, then the unit location is judged to be reliable.
If task 110 decides that the unit location is unreliable,
communication system 28 attempts to obtain location data which are
sufficiently accurate for the qualification of communication
services. Service is not necessarily denied if a mobile unit 24
provides fraudulent, inaccurate, or otherwise unreliable location
data. Rather, communication system 28 attempts to obtain reliable
and sufficiently accurate data. Accordingly, attempts at location
fraud are circumvented rather than being ignored or being merely
identified. The system-determined location is assumed to be
reliable because its calculation is more under the control of
communication system 28. However, the system-determined location
typically has a much larger error region associated with it than
the unit-determined location, particularly if the unit location has
been determined using satellite positioning system 26 (FIG. 1).
Process 104 performs a task 112 when the unit location is
unreliable. Task 112 gets a geolocation tolerance requirement. In
the preferred embodiment, this requirement may vary depending upon
a crude location analysis, such as may be provided by the system
location. When a mobile unit 24 may reside near a border or
boundary 38 (FIG. 2) and communication services are to be qualified
differently on different sides of the boundary 38, then a tighter
geolocation tolerance may be required. On the other hand, if a
mobile unit 24 appears to reside a long distance away from any
border or boundary 38, then a wider geolocation tolerance may be
tolerated. An appropriate tolerance may be obtained from a table in
response to the system-determined location.
After task 112, a query task 114 determines whether the
system-determined location error region betters the geolocation
tolerance obtained in task 112. In other words, task 114 determines
whether the actual location of mobile unit 24 most probably resides
within an error region defined by the geolocation tolerance. If
task 114 determines that the system location error region fails to
better the geolocation tolerance, then a task 116 repeats the
system location process (processes 64 and 66 combined, FIGS. 4 and
5) to gather more data on which to base location calculations and
thereby shrink the system location error region. Conventional
averaging and curve-fitting techniques may be used to combine the
additional data. Task 116 may achieve its goal in the preferred
embodiment within four iterations of the system location process.
Repetitions of processes 64 and 66 cause additional location
determination communications to be conducted between node 14 and
mobile unit 24.
After task 116 and when task 114 determines that system error
location betters geolocation tolerance on the first iteration of
the system location process, a task 118 is performed. Task 118
associates the system-determined location with user identity
information within communication system 28. As a consequence,
communication services offered to mobile unit 24 will be qualified
in response to the system-determined geolocation information.
As indicated in connection with task 110, when the unit-determined
location is judged to be reliable, a task 120 associates the
unit-determined location with user identity information within
communication system 28. As a consequence, communication services
offered to mobile unit 24 will be qualified in response to the
unit-determined geolocation information. System resources may be
consumed at a minimum rate due to the ability to rely upon
user-provided location data. Moreover, system access time will be
kept to a minimum due to reliance upon a single session of location
determination communication.
The program flow from task 110 to task 120 in FIG. 7 assumes that
the user-determined location has an error region associated
therewith which is sufficiently small to meet the tightest
geolocation tolerances imposed by communication system 28. This is
a typical situation, particularly when satellite positioning system
26 (FIG. 1) is used in the unit location process. However, if
another unit location process produces worse error regions, then a
process similar to tasks 114 and 116 may be included to achieve
acceptably accurate location data.
After task 118 or 120 assigns the appropriate location value for
use as system geolocation information, a task 122 continues the
system access process. Task 122 may grant or deny service based
upon the system geolocation information. After task 122, a task 124
may continue to provide communication services if system access
occurred above in task 120. Communication services may be provided
by establishing incoming or outgoing calls to mobile unit 24. After
task 124, program flow exits process 104.
In summary, the present invention provides an improved radio
telecommunication network with fraud circumvention registration.
The location determining process taught herein achieves the
desirable attributes of unit-based location determination without
making the system vulnerable to fraudulent location information.
Accurate location information is obtained through a fast location
determining and registration process which consumes a minimum of
system resources. The location determining and registration process
verifies the reliability of unit-provided location data before
relying on the location data. The location determining and
registration process also uses a system-based location
determination process as a backup to the unit-based location
determination process so that access is permitted in spite of
unreliable user-provided location information. Further, the
location determining and registration process uses a less precise
system-based location determination process to judge the
reliability of location information provided from a typically more
precise unit-based location determination process. In addition, the
location determining and registration process compensates for
inaccuracies caused by mobile units moving at high speeds.
The present invention has been described above with reference to
preferred embodiments. However, those skilled in the art will
recognize that changes and modifications may be made in these
preferred embodiments without departing from the scope of the
present invention. For example, the network with which the present
invention is used need not be global in scope and need not
incorporate satellite system nodes. Moreover, those skilled in the
art will appreciate that the processes and tasks identified herein
may be categorized and organized differently than described herein
while achieving equivalent results. These and other changes and
modifications which are obvious to those skilled in the art are
intended to be included within the scope of the present
invention.
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